This invention relates to a multifocal contact lens. More particularly, this invention relates to paired multifocal contact lenses.
Bifocal contact lenses are designed to correct or compensate for a condition of advancing age known as "presbyopia." In a presbyopic eye, the ability to focus at near distances, such as the normal reading distance, and in some cases at intermediate distances, is diminished. The loss of focusing capability is due to hardening of the eye's natural crystalline lens material.
Generally, multifocal contact lenses (usually either bifocal, trifocal or aspheric) are concentric or segmented in configuration. In a conventional bifocal contact lens of the concentric type, a first, centrally located, circular correction zone constitutes either distant or near vision correction, while a second annular correction zone surrounding the first zone provides the corresponding near or distance vision correction, respectively. In a conventional bifocal contact lens of the segmented or translating type, the lens is divided into two somewhat D-shaped zones. Usually the upper area is for distance vision correction, whereas the lower area is for near vision correction. Such conventional segmented contact lenses require some sort of movement of the lens relative to the eye to achieve acceptable visual acuity for both distant and near vision.
It has been discovered that as a presbyopic patient ages, there is generally little change in the prescription for the patient's distance vision (in healthy eyes). However, the near vision prescription requires continual correction. At some point in monovision corrective lenses, when the near vision prescription strength is increased beyond a certain level, it appears that the distance vision of the patient suffers.